As one type of radio-controlled timepiece that receives an external LF standard frequency and time signal and corrects the time, a master-slave time measurement system including a master timepiece that receives the LF standard frequency and time signal and a slave timepiece that communicates with the master timepiece via radio waves or electrodes and corrects the time on the slave timepiece is disclosed (see Japanese Unexamined Patent Application Publication No. 54-79680, Japanese Unexamined Patent Application No. 6-331762, etc.)
In such a master-slave radio-controlled time measurement system, the slave timepiece is often a watch. Specifically, in a place such as outdoors where the radio reception state is satisfactory, a radio-controlled watch receives a standard frequency and time signal using a built-in antenna and corrects the time.
On the other hand, in a building such as an apartment building or a steel-frame building where the reinforcing steel or steel frame functions as a shield and it is thus very difficult to receive radio waves indoors, the master timepiece is placed at a specific position such as a position near a window, at which radio waves can be received. This master timepiece receives an external standard frequency and time signal, whereas the slave timepiece receives radio waves emitted from the master timepiece and corrects the time.
In contrast, in the case of master and slave timepieces connected via electrodes, the master timepiece is placed at a position at which an external standard frequency and time signal can be received even being in the room. In order to correct the time on the slave timepiece, a terminal (electrode) of the slave timepiece is connected to a terminal (electrode) of the master timepiece. The master timepiece sends a time signal to the slave timepiece to adjust the time.
In such a master-slave radio-controlled time measurement system, the slave timepiece needs an antenna and an electrode to receive time information from the master timepiece. Compared with a general timepiece, the number of components is increased, and the configuration becomes more complex. As a result, cost is increased.
In order to provide the slave timepiece with an antenna, since the master timepiece emits the same signal as the external LF standard frequency and time signal, the slave timepiece must include a relatively large antenna capable of receiving such an LF standard frequency and time signal. Particularly in the case of a watch, reduction in size is difficult. In the case of an LF standard frequency and time signal, the length of one time signal (frame) is 60 seconds. When signals of two to three frames are to be received to determine whether the correct time signal is received, it takes approximately two to three minutes only to receive the signals. It thus requires time to adjust the time.
When the master timepiece and the slave timepiece have corresponding electrodes, the electrodes are exposed to the outside. As a result, their waterproof abilities become degraded. A watch or the like must include covers for the electrodes. As a result, the number of components is increased, and cost is further increased.
An object of the present invention is to provide a time measurement system including such master-slave timepieces in which increases in the number of components and cost are suppressed, the time is adjusted within a short period of time, and waterproof abilities of the master-slave timepieces are improved, and to provide a method of controlling the same.